1. Field of the Invention
The present invention relates generally to post die singulation of wafers, and more particularly, relates to separation of dice from wafer saw tape while substantially retaining the orientation die during separation.
2. Description of the Related Art
Semiconductor Integrated Circuits (ICs) are typically fabricated in wafer form on wafer saw tape. After fabrication, using precision cutting techniques, individual die are cut or singulated from the wafer without cutting through the saw tape. In the past, where the precise orientation of the die was necessary, a tape and reel assembly was typically applied to transport the chips to the individual processing stations. The tape and reel assembly includes a tape with a plurality of transport cavities spaced at regular intervals. Once a chip has been placed inside a transport cavity, the cavity is sealed with an adhesive tape so the chip can be safely transported from station to station by the tape and reel assembly. However, to transfer chips singulated from a wafer into the cavities of the tape and reel assembly, special devices, known as device transfer machines were used.
As shown in FIG. 1, these special transfer machines 15 are responsible for transferring and flipping a semiconductor device, such as a flip chip die 16, from a singulated wafer to a transport cavity 17 which is part of the tape and reel assembly 18. The transfer to the transport cavity 17 is complicated by the small size, delicacy and orientation of the die 16. An exemplary flip chip die may be about 35 mils square, which limits the applicable handling techniques. In addition, after singulation, the die is precisely oriented with its solder bumps facing up. However, in order to mount the die, it has to be placed in the transport cavity with the solder bumps facing downward.
Typically, the transfer machine 15 includes a robotic loading arm or another suitable pick and place mechanism 19 that precisely picks and places the die 16 from the wafer saw tape 20. The loading arm 19 usually includes a head housing a vacuum tube that applies a vacuum pressure on the support surface of the die between the solder bumps to transport the die from the saw tape 20 to the transport cavity 17. To dislodge the die from the adhesive of the wafer saw tape 20, however, the vacuum tube approach alone is usually insufficient.
One technique and apparatus applied to separate the adhered die from the saw tape 20 is to apply a needle push-up system 21 with vacuum assistance to facilitate retention of the wafer saw tape during the push-up procedure. As shown in FIG. 2, when a selected die 16 is properly positioned over the push-up system 21, a push-up needle 22 thereof moves the die 16 upwardly and partially separates the die from the wafer saw tape 20 from underneath. When the push-up needle 22 begins pushing the single die 16 upward from below, the vacuum assistance commences to retain the saw tape 20 surrounding the die against the support surface 25. The saw tape 20 is then peeled off the die backside, releasing the adhered die. Subsequently, a robotic loading arm 19 picks the die and places it in the transport cavity.
Before placement of the die 16 in the transport cavity 17, however, the loading arm 19 must flip the die 16 over for proper positioning in the transport cavity 17. The transfer machine 15, thus, typically includes a flipper mechanism 26 that works in conjunction with the loading arm. In the past, the loading arm 19 picked the separated die 16 and placed it on a platform of the flipper mechanism 26, which then rotatably flipped the die over. Once flipped, as simplified in the following description, the platform would release the flipped die into the transport cavity for future chip processing. More recently, the loading arm places the separated die into a station of a multi-station rotary die handling device which significantly improved the flipping capacity. This design is the subject of U.S. Pat. No. 6,364,089 which is incorporated by reference in its entirety.
While these current device transfer machines adequately perform their respective functions, they are problematic for a number of reasons. For example, the needle push-up technique applied to remove the die adhered to the wafer saw tape is slow, tedious and complex. Depending upon the height and weight of the dice, certain parameters require proper adjustment such as pick and bond forces, height adjustment, etc. Due to such complex physical demands and restraints, a bulk removal approach of the dice from the wafer saw tape cannot be accommodated. This represents a significant bottleneck in the overall IC testing and packaging sequence.
In view of the foregoing, a device transfer machine with improved throughput would be desirable.